This invention relates to a wind turbine for generating electrical power.
Conventional power generating plant, such as coal and oil fired plant, use hydrocarbon fuels to generate electricity. Burning hydrocarbons both uses up valuable non-renewable resources and adds chemical pollutants to the environment. Thus there is a need to harness natural energy for conversion into electrical energy.
Natural energy sources include water, in the form of hydroelectric power, and wind. Hydroelectric power is available in areas with favorable geography such as found in Norway where hydroelectric power makes a significant contribution to Norway's energy needs.
Wind turbines are used to convert wind energy into electrical energy that is typically fed into the grid. However, wind turbines are vulnerable to severe damage caused by high winds. Specifically, in high winds a wind turbine may experience a run-away incident in which the blades of the wind turbine rotate at a destructive rate. Various expensive and complicated design solutions have been applied to wind turbines to avoid run-away incidents.
In one type of wind turbine the rotation rate of rotor blades is monitored and after a predetermined point a control system applies a braking force to the rotor assembly to inhibit or stop the rotation of the rotor blades. Since the brakes are typically applied when the rotor blades are near their maximum permitted rate of revolutions, failure in the braking system can lead to a run-away incident and the destruction of the wind turbine.
The American farm windmill design limits the effect of high winds by using a tail vane which, when triggered by wind speeds exceeding its maximum set point, turns 90 degrees with respect to the turbine shaft in order to rotate the turbine out of the wind. The 4-arm Dutch windmill relies on manual furling of canvas sails to accomplish the same effect. While such design solutions may help to avoid run-away incidents, rotating the turbine completely out of the wind stops the conversion of wind energy into electrical energy.
U.S. Pat. No. 4,333,018 issued Jun. 1, 1982 to Bottrell, describes a downstream wind turbine that converts wind energy into controlled wind turbine torque for generating electrical energy. Like other downstream wind turbines, the '018 wind turbine is normally oriented downwind of the turbine tower, so that wind forces acting on the wind turbine create a drag which keeps the wind turbine directed into the wind, but downstream from the turbine tower. The '018 wind turbine comprises a yaw control vane which is used to partially rotate the wind turbine out of a high wind to maintain a constant turbine torque. Rotating the turbine partially out of the wind creates additional stresses on the wind turbine.
U.S. Pat. No. 4,449,889 issued May 22, 1984 to Belden, describes a windmill having a plurality of blades generally transverse to an upstanding rotor shaft. The blades have an airfoil cross-sectional shape and are oriented with a negative angle of attack, thereby allowing the leading edge of the airfoil to turn into the wind. The windmill preferably has a tilting assembly that tilts the rotor shaft and blades at an angle dependent upon the velocity of the wind. As the wind velocity increases the rotor shaft is automatically tilted into a vertical position by the control tail. This automatic tilting of the windmill provides automatic control of the rotor speed. The rotor blades are preferably pivotally connected to the rotor shaft. Rotating the turbine partially out of the wind creates additional stresses on the wind turbine; rotating the turbine completely out of the wind stops conversion of wind energy into electrical energy.
U.S. Pat. No. 4,352,629 issued Oct. 5, 1982 to Cheney, Jr., describes a wind turbine of the type having an airfoil blade mounted on a flexible beam and a pitch governor which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch. A limiter restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows twisting of the beam by the governor under excessive wind velocity conditions to orient the blades in stall pitch positions, thereby preventing run-away operation of the turbine. In the preferred embodiment, the pitch governor comprises a pendulum which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment. The '629 solution is complex and relies on twisting a flexible beam, which must be designed to cope with such twisting thereby adding to manufacturing cost.
In addition to run-away issues, gyroscopic precession can cause severe loads on wind turbines. Precession is a phenomenon that effects rotating bodies, wherein an applied force is manifested 90 degrees later in the direction of rotation from where the force was applied. A change in wind direction causes precession, wherein the rotor blades (which form part of the rotor assembly) experience forces that cause them to tilt upward or downward depending on the change in wind direction and direction of rotation of the blades. For example, with respect to a downstream wind turbine, if the rotor blades are rotating clockwise and the wind direction causes the rotor assembly to turn to the right with respect to original wind direction, the rotor blades will want to tilt downwards. If the rotor blades are rotating clockwise and the wind direction causes the rotor assembly to turn to the left with respect to the original wind direction then the rotating blades will want to tilt upwards.
Wind turbines not designed to handle precession risk serious damage. Various solutions have been applied to counter precession. One solution relies on using turbines that always point in one direction. Such design solutions are at best limited in scope and are not suitable for most areas where wind direction is variable.
Some wind turbines are designed to respond slowly to wind direction changes thereby limiting the gyroscopic precession forces. Such systems require gears and drive mechanisms to make controlled slow turns. Such mechanisms add to manufacturing and maintenance costs; in addition, a drive motor might be required to drive the mechanism. Wind turbines fitted with such mechanisms are also less efficient since they are necessarily slow in responding to changes in wind direction.
Some manufacturers of wind turbines deal with precession effects by preventing tilting of the rotor assembly. Such wind turbines still experience the up and down tilt forces in the rotor assembly but incorporate, for example, very strong support towers that are able to withstand the precession forces transmitted to the support tower from the rotating blades. Such wind turbines are very expensive to build since they require a considerable amount of strengthening and use of expensive parts. In addition, the rotator blades will experience severe flexing forces necessitating expensive development and high manufacturing costs.
In another design solution, the rotor attached to the blades is allowed to teeter separately from the rest of the rotor assembly thereby at least partly isolating the support tower from the effects of gyroscopic forces. Teetering blades can strike the support tower destroying the turbine.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a wind turbine solving the aforementioned problems is desired.